ASK TOM WHY

Some scientists theorize that global warming could eventually lead to development of a mini ice age. Please explain how global warming could develop a cold period on Earth.

Jim N. Tone, Lexington, Ill.

Dear Jim,

The Gulf Stream carries massive amounts of tropical heat northward into the North Atlantic Ocean. That heat is lost to the Northern Hemisphere atmosphere and is primarily responsible for the relatively mild climate that Europe and eastern North America experience. After losing its heat and cooling, North Atlantic water sinks into the ocean depths and returns south. However, it is theorized that as the climate warms, fresh (salt-free) and consequently lighter meltwater from the Greenland ice cap will flood into the North Atlantic. Because of its freshness, the meltwater will not sink--thereby disrupting the Gulf Stream flow that helps to warm the Northern Hemisphere.

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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.